Saving data and database storage are functions of Formidable Forms, not PRO2PDF. This sounds like an issue for the outstanding Formidable Forms support.
Let us know if PRO2PDF is causing any issues. However unlikely, to test, deactivate PRO2PDF and test multiple submissions if the issue goes away let us know by completing this form and you’ll need to include FTP credentials for us to troubleshoot a database issue.
We remain at your service.